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Updated: Mar 18, 2026
In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy
Published on: July 2, 2021
Impingement in Patients With Femoroacetabular Impingement Syndrome Routinely Occurs Below 90° of Hip Flexion
Benjamin T Johnson1, Collin D R Hunter1, Allan K Metz1
1Department of Orthopaedics, University of Utah, Salt Lake City, Utah, U.S.A.
Purpose:
To determine the angle of hip flexion at which femoral neck chondral lesions in patients with femoroacetabular impingement syndrome (FAIS) engage the labrum under direct arthroscopic visualization.
Methods:
Primary hip arthroscopy patients between 2022 and 2024 with intraoperatively identified femoral neck chondral lesions were included. Patients were flexed at the hip with the lower extremity in neutral rotation until the labrum engaged the femoral neck chondral lesion. Lateral photographs of the patient on the operating table were taken at this position, and degree of hip flexion was calculated using an online goniometer. Comparisons between the angle of impingement and patient demographics were assessed via two-tailed t-tests and one-way analysis of variance. Regression analysis was performed to evaluate the relationship between the impingement angle and various radiographic measurements while controlling for age, sex, and body mass index (BMI).
Results:
A total of 108 patients were analyzed in this study. Mean age was 31.0 ± 10.8 years, mean BMI was 26.4 ± 5.8 kg/m2, and 73 (68%) were females. Mean angle of hip flexion required to achieve impingement was 63.3° ± 11.5° (range: 39.8-94.9). Males engaged at higher flexion angles (66.5° ± 10.9°) compared to females (61.8 ± 11.6, P = .045). Regression analysis had inverse relationship between impingement angle and alpha angle on frog leg lateral (β = -0.291, 95% confidence interval [-0.427 to -0.153], P < .001) and anteroposterior radiographs (β = -0.393, 95% confidence interval [-0.567 to -0.231], P < .001), as well as a direct relationship between femoral version and impingement angle (β = 0.406, 95% confidence interval [0.395 to 0.985], P < .001).
Conclusions:
Hip impingement in those with FAIS may routinely occur at hip flexion angles below 90° in neutral rotation, with males engaging at higher flexion angles than females. Furthermore, the angle of impingement directly correlates with femoral version and inversely correlates with alpha angles on radiographs.
Level Of Evidence:
Level IV, case series.
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